Something similar has come up before with people swapping engines from cars not on the same line but are the exact same thing between different cars, and it was ruled OK. Such as SR20DE engines coming in a Sentra SE-R but the same thing is in an Infiniti G20.
Pretty sure it was Matt Kogan 4-5 years ago who got a ruling from Doug Gill for his STS SE-R which had an engine from a G20. Yeah that's STS, but if it's OK for ST, shouldn't be any different than SP. Same exact engine in both cars from '91 through '93. Only difference is the valve cover -- one has "Nissan" cast on the outside of the valve cover, the other has "Infiniti."
It shouldn't be any different for a transmission. As long as the transmission is *exactly* the same, it should be OK. Gearing, case, etc. If something minor like a speedo sensor hole is in a different location, then the transmission is NOT exactly the same.
Pat
'92 Sentra SE-R, daily driver and track car
'82 Camaro Z28, ESP, 65% prepared, 50% ownership
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